Relay control circuit having time delay means



G. L. BORELL 3,214,643

RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS Oct/26, 1965 2Sheets-Sheet 1 Filed Feb. 14, 1962 INVENTOR. GEORGE .4. 50/9514 11TTORNE Y5 ca. L. BORELL 3,214,643

RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS Cat. 26, 1965 2Sheets-Sheet 2 Filed Feb. 14. 1962 F R M W WM 70 N m 0 U m B mm A K M WI P vm. WW 9N w N G N fi W \N N\ QM Q sm 1! TTORNE Y5 United StatesPatent i 3,214,643 RELAY CONTROL CIRCUIT HAVING TIME DELAY MEANS GeorgeL. Borell, Glen Rock, NJ. Almo Laboratories Co., Inc., 424 Madison Ave.,New York, N .Y.) Filed Feb. 14, 1962, Ser. No. 173,201 3 Claims. (Cl.317141) This invention relates to systems for controlling the deliveryof a liquid material to a remote location where the amount of materialso delivered is critical.

In general, the invention contemplates a system for replenishing incontrolled amounts a liquid constituent of a bath in which the liquid isbeing progressively consumed and in particular one which automaticallymaintains a desired concentration of the liquid in the bath unless suchmaintenance is for some reason impossible of fulfillment in which casethere is afforded a sensible indication.

The particular embodiment of the invention which is hereafter disclosedrelates to dishwashing machines and employs the electrolytic propertiesof the detergent in the wash tank of the machine to detect andcompensate for an insufiicient supply in the tank that is available foruse in the washing operation. Because the new supply of detergent is notinstantaneously so available on introduction to the tank even though thequantity may be suificient in amount to ultimately raise theconcentration to the desired level, a time interval must be afforded tomeasure its uniform concentration. To this end the delivery is made insmall increments or shots and after each shot the control system isreset for its succeeding one if necessary. This cycling operation of thesystem introduces a delay in the oif-to-on interval which afiords sometime for a blending of the detergent in the wash water and hence a moreaccurate measurement of its true concentration. The principal advantageof cycling the delivery of the detergent to the wash tank is theprevention of excessive overshooting which would be present if thedelivery were continuous.

A circuit supplied by an A.C. source has a pair of elec trodes in thewash tank which are made responsive to the conductivity of the washsolution as determined by the concentration of the detergent thereinserving thereby to start the supplying of new detergent. A separateconductivity device in the detergent supply for stopping the delivery ofdetergent is dispensed with and in lieu thereof heat responsive elementsare placed in the circuit for adjusting the impedance of the sensingcircuit and thereby timing the feeding of detergent material to thetank. One of the thermal timing elements is a bimetallic switch whichcloses on cooling in the oif-to-on interval thus affording a time delayfor blending the detergent in the wash water as aforementioned. Theswitch is connected in series with and between the conductivity deviceand a bridge-type rectifier in the circuit and, therefore, passes anA.C. current which is desirable for the elimination of arcing. Shuntingthe switch is a hot wire resistor which is the second thermal timingelement in the circuit. This element is placed in the circuit in effectwhen the switch is broken and increases in impedance as its temperaturerises during the on cycle. It is thus seen how the two thermal timingelements act cooperatively and sequentially to determine the length ofthe feed cycle.

A smoothing capacitor is a third timing element in the control circuitbeing employed to introduce a delay between feed cycles. This element isdisposed in the rectifier output and across the relay coil which is incontrol of both the heater for the bimetallic switch and the detergentfeed apparatus. Its primary function is to smooth the current in therelay to prevent it from chattering.

3,214,643 Patented Oct. 26, 1965 In addition, its capacitance issutficiently large that it introduces a time delay during its rechargingphase which starts at the termination of the feed cycles at which pointthe impedance in the control circuit is maximum and the voltage acrossthe capacitor is minimum. The additional delay introduced by thecapacitor during the offto-on cycle permits the blades of the bimetallicswitch to return to near normal pressure and the resistor to return tonear ambient temperature state before the cycle can be repeated andthereby affords the detergent feed apparatus sufiicient time to respondreliably to the relay control and stabilizes the mechanical operation ofthe switch. These elements are the sole components for the control of asingle relay which in turn causes the cycling operation of the detergentfeed apparatus. Since the elements are electrical and not electronic orthermionic in nature, they can be expected to have long life and bedisposed in a circuit of relatively simple and economic arrangement.

The use of a single conductivity device permits the delivery to be madedirectly from the original shipping container for the detergent which isparticularly advantageous if the detergent is in liquid form since apowder detergent would have to be dissolved and dispensed from aseparate container or transferred to the hopper of a dry-feedingmechanism. The action of these elements in response to heat yields apredetermined amount of detergent material during the initial cycle ofoperation. This amount is diminished once the thermal elements areheated and the delay inherent to their operation is thereby shortened.The shortened feeding cycles are constant for the entire remainingperiod of operation. Between cycling periods the thermal elements returnto ambient temperature so that the initial feed cycle in the succeedingperiod will be normal and the remaining feed cycles uniformly shortened.

In addition the system employs visual and audible signals for thepurpose of affording conspicuous indication of specific untowardoperating conditions in the system. The circuit elements are soconstituted and arranged, for ex ample, that the signals will rapidlycycle on and off after the first cycle if excessive dilution isoccurring in the wash tank but will, on the other hand, lock in forcontinuous indication if the supply of detergent has been exhausted.Largely because of the stabilizing effect of the smoothing capacitor onthe bimetallic switch, the audible indicator may be mounted directly onthe chassis of the control system since any vibration in the chassisresulting from the indicators operation will not unduly impair theoperating efficiency of the switch. Because the cycling is actuatedsolely by electrical timing elements rather than by change in liquidlevel, as in prior systems, the cycling is more readily distinguishableand, hence, more attention demanding.

One object of the invention is to provide a control system, which isboth durable and economic to produce and operate, and which functionsefiiciently to effect the delivery in discrete increments of a liquidmaterial to a bath.

Other features and advantages of the invention will appear from thefollowing description of the embodiment illustrated in the drawings, inwhich FIG. 1 is a sectional elevation of the Wash section of the washtank and the detergent dispensing container from which liquid detergentis pumped into the wash tank, together with the control box in which theelectrical control system for maintaining the desired detergentconcentration is arranged, and

FIG. 2 is a diagram of the electrical control system.

A tray of dishes 1 is shown in the wash section of a dishwashingmachine, on a conveyor which carries the tray to the rinse section onthe right (not shown). Water containing detergent is pumped from thewash tank 2 and delivered forcibly upon the dishes through the spraymeans 3. An overflow pipe 4 determines the level of the water in tank 2.A drain board 5 leads the water which is delivered to the rinse sectionby pipe 6 from the rinse section into tank 2, or, as often is the case,into another tank which overflows into the wash tank. In large machinesthere are more than one tank receiving the rinse water and progressivelyoverflowing one into another and eventually into the wash tank.

This constant addition of clean water to the wash tank dilutes thedetergent concentration and periodically more detergent has to be addedto the wash water. This is done automatically from a liquid detergentcontainer disposed on the floor below the wash tank, the liquiddetergent being forced by pump 8 through a hose 10 connecting thecontainer 7 to the wash tank 2. The pump is controlled by a motor 11which is actuated by the electrical control system.

To detect or sense the conditions in the wash tank 2, a pair of closelyspaced electrodes 12 which are adapted to contact the contents in thewash tank and will be conductively bridged by the liquid which willafford a resistance which will vary inversely with the alkaline ordetergent content of the liquid. The electrodes 12 in the tank 2 aresuitably insulated and supported in a Well of the 'tank proximate theoutlet opening in the tank for the liquid detergent.

Whenever the conductivity of the wash water in the tank reaches acertain minimum degree, it causes the pump to be actuated, as we shallsee, to admit liquid detergent from the wash tank to the container 7. Asconductivity in the tank increases due to the admission of detergent,the resistance across the electrodes 12 is reduced until delivery to thetank is shut off. As mentioned the delivery is made in predeterminedincrements and will continue in a cycling operation involving the makingand breaking of a switch in series with the motor 11 until the selectedconditions in the tank are satisfied. This cycling may continueindefinitely if water is being delivered from the rinse sec- .tion atsuch a rate that the desired detergent concentration cannot be effectedand the cycling will cease altogether and the motor operatedcontinuously if the detergent becomes entirely exhausted in thecontainer 7, appropriate signals being provided so that the operator canreadily determine the operation of the motor driven pump and distinguishthereby the specific reasons why the desired detergent concentration inthe tank is incapable of attainment.

The electrical circuit by which the pump is controlled and maintenanceof the desired detergent concentration in the wash tank is efiected isdiagrammatically shown in FIG. 2.

It is a low voltage system fed by a low voltage transformer 13 which isa voltage step down instrument having a 22-volt secondary and a 115-voltprimary. The transformer can, of course, be designed with a 230-voltprimary if required. Wires 14 and 15 constitute the two .sides of thesupply line and electrodes 12 are connected across the line in serieswith a variable 100-ohm resistor 16 and a ZO-ohm resistor 17 whichdetermine the distribution of the voltage drop in the connection acrossthe line including the electrodes. A switch 18 is disposed in the wire14 connected to the secondary of the transformer and a pilot light 20and current limiting resistor 21 are connected in series with the switch18 and across the secoperation employed in some previous designs. Acapacitor 26 is connected in shunt with the relay 23 to smooth out thepulsating rectified voltage and serves to prevent relay chatter.

The control relay 23 includes a contact 27 which is connected by wire 28to one side of the supply line and which is adapted to contact aterminal on conductor 29 which is connected to the other side of thesupply line. A thermal element 30 of thermal time-delay relay 31 isdisposed in the line connecting conductor 29. A normally closedbimetallic switch adapted to open when heated is a second element of thethermal time-delay relay 31 and the two elements of this device areenclosed by a sealed envelope. The bimetallic switch 9 is connectedbetween one side of the electrodes 12 and the full wave rectifier 22.Shunting the thermal time-delay relay 31 and connected between thesensing electrodes 12 and the full wave rectifier 22 is incandescentlamp 33. This lamp has a filament 33a which is a hot Wire resistor, itstemperature response establishing a 200 ohms resistance at coldtemperature and a 500 ohms resistance at hot temperature. The motor 11for the pump 8 is connectable across the supply line by the relay 23,one lead for the motor 11 being connected to the wire 14 of the supplyline and the other lead for the motor being connected by conductor 34 tothe terminal of the conductor 29 which, on energization of the relay, isengaged by contact 27 to connect the motor .to wire 15 on the other sideof the supply line.

Also connectable across the supply line through the switching elementsof the relay 23 is the signal bell 35 and signal light 36, theseindicators being connected on one side to the wire 14 and to theswitching elements of the relay 23 on the other side by the conductor34.

It will be seen, therefore, that in operation there is a succession ofshots of a small quantity of liquid detergent delivered into the washtank 2, from the detergent container 7 until an alkaline condition isreached where the drop across the electrodes 12 is no longer sufficientto energize the relay 23 and energize the motor 11 for the pump 8. Wherea succession of shots is required, the drop across the electrodes 12continues within the relay energizing range. Each delivery shotcorresponds to a cycle of operation of the thermal time-delay relay 31and the incandescent lamp 33 during which the bimetallic elements of theswitch 9 of the time delay-relay 31 initially carry the full current atpractically no impedance, the current, however, being subsequentlycarried by the shunting, incandescent lamp 33 as the impedance acrossthe bimetallic elements increases to infinity. Since the resistance ofthe hot wire resistor 33a increases to about 500 ohms at the end of thecycle, the current through the relay coil 24 will be reduced at the endof each cycle. Whether the current is sufliciently reduced to cause therelay to open its switching elements depends on the voltage drop acrossthe electrodes 12. Except under the specific condition that thedetergent has been exhausted, the current will be sufficiently reducedto open the switching elements so that the thermal time-delay relay 31will be reset for the succeeding cycle. On the first feed cycle, therewill be required approximately three seconds for the relay to open andan additional three seconds for the hot wire resistor of the lamp 33 tobe heated up to full ohmage. On every succeeding feed cycle, includingthe final one, the total time for this to occur will be about twoseconds since both elements have been preheated. The time intervalbetween rapidly for two second intervals. If the cycling continues for aperiod of time, it will aiford an easily recognizable indication thatthe detergent delivery to the wash tank is being excessively diluted bythe water going in from the rinse section of the apparatus, or that afillvalve is open inadvertently.

Because it has been found that in dishwashing machines having anautomatic detergent feed control for liquids, there is no ready meansfor easily determining that the detergent container has becomeexhausted, it was found desirable to provide a signal to indicate thisparticular fact. To this end, it will be seen that the signal indicatorsare locked in continuously instead of cycling when the liquid detergentis exhausted. This is accomplished because the voltage drop across theelectrodes becomes very large when there is a Weak detergent solution inthe wash tank and, as a consequence, the current through the relay 23increases to the point where the switching elements of the relay arecontinuously closed even though the hot wire resistor is at its maximumresistance. Accordingly, a continuous ringing of the bell and acontinuous illumination of the lamp 36 will give an easily identifiedindication that the liquid detergent supply is exhausted.

While the particular embodiment which has been above described and shownin the drawings has proven satisfactory, the invention may be otherwiseembodied without departing from its scope as defined in the followingclaims.

What is claimed is:

1. A time delay circuit means comprising a conductivity sensing device,a rectified control circuit connected to said conductivity device and toa load control means, said circuit including a relay in control of theload control means, and said conductivity sensing device forestablishing the relay in one state for a given interval of time,causing said relay to change to its opposite state at the end of thegiven interval of time, and circuit breaking means for affording a timedelay in returning the relay to said one state but for a diminished timeinterval, said load control means having a thermal control element incontrol of said delay means.

2. A time delay circuit means comprising a set of sensing electrodes, arectified control circuit connected to said electrodes and to a loadcontrol means, said circuit including a supply, said electrodes and avoltage distributing resistor connected across said supply, a full waverectifier connected in parallel with said electrodes, a delay having athermal responsive element connected between said electrodes and saidrectifier and a bimetallic switch shunting said thermal responsiveelement, a heater in control of said bimetallic switch, a relay switchin control of said heater, a relay adapted to operate said relay switchand connected to the output of said rectifier and a smoothing capacitordisposed across said relay.

3. A time delay circuit means comprising a set of sensing electrodesadapted to contact a solution in a tank, and a control circuit connectedto said electrodes and to a load control means, said circuit including asupply, said electrodes and a voltage distributing resistor connectedacross said supply, a full wave rectifier connected in parallel withsaid electrodes, a delay having a hot wire resistor with a positivethermal coefiicient connected between said electrodes and said rectifierand a thermal time-delay relay having a bimetallic switch connectedacross said hot wire resistor and a heater in control of said bimetallicswitch, a relay switch connectable across the supply and in control ofsaid heater, relay means connected across said rectifier and operativeto control said relay switch and a smoothing capacitor disposed acrosssaid relay means.

References Cited by the Examiner UNITED STATES PATENTS 2,476,329 7/49Sitzer 317-132 2,476,330 7/49 Sitzer 317-132 2,482,820 9/49 Wolfson eta1. 307-132 2,593,825 4/52 Albrecht 137-95 2,672,188 3/54 Cassidy317-132 2,786,968 3/57 Kabak 323-68 2,817,806 12/57 Borell 317-1412,830,615 4/58 Borell 137-392 2,832,068 4/58 'Warren 317-132 2,932,7744/60 Rice 317-141 3,017,564 l/62 Barney 323-68 3,067,410 12/62 Louis317-132 SAMUEL BERNSTEIN, Primary Examiner.

ISADOR WEIL, NEIL C. READ, MAX L. LEVY,

Examiners.

1. A TIME DELAY CIRCUIT MEANS COMPRISING A CONDUCTIVITY SENSING DEVICE,A RECTIFIED CONTROL CIRCUIT CONNECTED TO SAID CONDUCTIVITY DEVICE AND TOA LOAD CONTROL MEANS, SAID CIRCUIT INCLUDING A RELAY IN CONTROL OF THELOAD CONTROL MEANS, AND SAID CONDUCTIVELY SENSING DEVICE FORESTABLISHING THE RELAY IN ONE STATE FOR A GIVEN INTERVAL OF TIME,CAUSING SAID RELAY TO CHANGE TO ITS OPPOSITE STATE AT THE END OF THEGIVEN INTERVAL OF TIME, AND CIRCUIT BREAKING MEANS FOR AFFORDING A TIMEDELAY IN RETURNING THE RELAY TO SAID ONE STATE BUT FOR A DIMINISHED TIMEINTERVAL, SAID LOAD CONTROL MEANS HAVING A THERMAL CONTROL ELEMENT INCONTROL OF SAID DELAY MEANS.